This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application 2000-283539 filed on Sep. 19, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a vehicle hydraulic brake apparatus. More particularly, the present invention pertains to a hydraulic pressure assisting device for a vehicle hydraulic brake apparatus.
Various types of hydraulic pressure assisting devices provided for vehicle hydraulic brake apparatus are known, including, for example, hydraulic pressure boosters. A so-called direct-acting type hydraulic pressure booster is disclosed in a Japanese Patent Application published as Toku-Kai-Hlei 2 (1990)-060871. This known hydraulic pressure booster includes an input shaft and a plug disposed along a housing. A hydraulic passage is axially defined in the input shaft. An annular groove is defined between two sealing members disposed in the plug. The booster is designed so that hydraulic fluid is ejected to a reservoir through the passage of the input shaft and the annular groove.
U.S. Pat. No, 4,548,037 discloses a hydraulic power booster constituting a hydraulic pressure assisting device. This known hydraulic power booster includes an input piston and a boost piston. A reservoir chamber is defined between a sealing member disposed in the respective input piston and the boost piston. This booster is designed so that hydraulic fluid is ejected to a reservoir from the reservoir chamber through an exhaust port.
The hydraulic pressure booster disclosed in the aforementioned Japanese Patent Application published as Toku-Kai-Hei 2 (1990)-060871 includes two sealing members disposed in the plug adjacent to the housing. For that reason, an axial distance between these two sealing members is required to have a maximum length corresponding to the slidable movement of the input shaft or input member. Further, an extending portion of the input shaft that extends outwardly from the position of one of the sealing members is required to have the maximum length of the slidable movement of the input shaft. Thus, the actual length of the input shaft may be at least twice as long as the maximum length of slidable movement thereof. As a result, the hydraulic pressure assisting device is quite long, thus providing a device having an excessively large size.
With respect to the hydraulic power booster disclosed in the aforementioned U.S. Pat. No., 4,548,037, the reservoir chamber is mechanically expanded and reduced in response to movement of the input piston. The sealing member disposed in the input piston is slidably moved at the inner surface of the housing. Therefore, it may be necessary to manufacture the inner surface of the housing and the input piston to possess high durability characteristics, thus increasing the manufacturing cost.
As described above, it thus seems that the vehicle hydraulic brake apparatuses are susceptible of certain improvements with respect to being provided with an improved hydraulic pressure assisting device that reduces the slidable moving portion of the sealing member, reduce the length of the hydraulic pressure assisting device, and is manufactured at a low cost.
A hydraulic pressure assisting device for a hydraulic brake apparatus of a vehicle includes a power piston slidably accommodated in a housing, an input member movable relative to the power piston in response to operation of a brake operating member, an auxiliary hydraulic pressure source, a pressure modulating device, and a cylindrical elastic member. The auxiliary hydraulic pressure source increases brake fluid in a reservoir to a predetermined pressure and outputs power hydraulic pressure. The pressure modulating device is connected to the auxiliary hydraulic pressure source and the reservoir for modulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a predetermined pressure corresponding to movement of the input member relative to the power piston and for supplying the modulated power hydraulic pressure to a power chamber in the power piston. The cylindrical elastic member has one opening end portion connected to the input member and another opening end portion connected to the housing. A space defined in the cylindrical elastic member is connected to the pressure modulating device and the reservoir.
Alternatively, the one opening end portion of the cylindrical elastic member can be connected to the power piston while the other opening end portion is connected to the housing, with the space defined in the cylindrical elastic member once again being connected to the pressure modulating device and the reservoir.
The hydraulic pressure assisting device can also include a solid covering member that covers the cylindrical elastic member and the inner space of the solid covering member, with the solid covering member being approximately in contact with the outer surface of the cylindrical elastic member.